1. Field of the Invention
The present invention relates to disk drives. In particular, the present invention relates to servo writing a disk drive by overwriting a harmonic frequency fill pattern in the servo burst area.
2. Description of the Prior Art
FIG. 1 is a prior art recording format showing a plurality of embedded servo sectors 20–2N recorded on the disk 4 of a disk drive which define a plurality of radially-spaced, concentric data tracks 6. Each data track 6 is partitioned into a plurality of data sectors wherein the servo sectors 20–2N are considered “embedded” in the data sectors. Each servo sector (e.g., servo sector 24) comprises a preamble 8 for synchronizing gain control and timing recovery, a sync mark 10 for synchronizing to a servo data field 12 comprising coarse head positioning information such as a Gray coded track addresses for use during seeking, and servo bursts 14 which provide fine head positioning information for use during tracking. In a “headerless” format, the servo data field 12 also includes information identifying the data sectors between the servo sectors.
The servo sectors 20–2N may be written to the disk 4 using the head 16 internal to the disk drive, for example, using an external servo writer or a self-servo writing technique. The head 16 is attached to a distal end of an actuator arm 18, which is rotated about a pivot 20 in order to position the head 16 radially over the disk 4 while writing the servo sectors 20–2N. The servo sectors 20–2N form arcuate servo wedges extending from the outer diameter to the inner diameter of the disk 4. Alternatively, the servo sectors 20–2N may be written to the disk 4 by a media writer employing a linear actuator such that the servo wedges are substantially linear, wherein the disk 4 is inserted into the disk drive after servo writing by the media writer.
During a self-servo writing operation, as well as during normal operation of the disk drive, the actuator arm 18 is rotated about the pivot 20 by a rotary actuator. The rotary actuator comprises a voice coil having a first leg 22A and a second leg 22B coupled to the end of the actuator arm 18. When the voice coil is energized with current, the resulting magnetic flux interacts with the magnetic flux of permanent magnets (not shown) to create a torque that rotates the actuator arm 18 about the pivot 20.
In conventional longitudinal magnetic recording the area between the servo bursts 14 is typically DC erased when servo writing the servo sectors 20–2N. However, DC erasing the area between the servo bursts 14 adversely affects the reproduction signal when using more recent perpendicular magnetic recording techniques. A DC erased area induces a DC offset in the read signal as well as an inter-track interference which degrades the position error signal (PES) generated from reading the servo bursts.
U.S. Patent Application No. 2002/0057509 discloses a technique for servo writing a disk drive by writing an AC signal in the area between the servo bursts at a frequency higher than the servo burst frequency. The servo bursts and AC signal are written during each revolution of the disk using a well known “trimming” technique. The frequency of the write clock is adjusted on-the-fly such that there is essentially no phase shift between the servo burst signal and AC signal. However, this technique may not be suitable to servo write the servo bursts if the well known trimming technique is not used. That is, it may be desirable to write servo bursts of a current servo track without trimming the servo bursts of a previously written servo track.
There is, therefore, a need to servo write a disk drive using perpendicular magnetic recording without trimming the servo bursts.